3章

/*简单的猜数游戏 */
#include<stdio.h>
int main(void)
{
    int  mynumber=38;
    int  yournumber;


    printf("Input your number:");
    scanf("%d",&yournumber);
    if(yournumber==mynumber)
        printf("Ok! you are right!\n");
    else
        if(yournumber > mynumber)
            printf("Sorry! your number is bigger then my number!\n");
        else
            printf("Sorry! your number is smaller than my number!\n");


    return 0;
}

/* 输入一批学生的成绩， 计算平均分， 并统计不及格成绩的学生人数 */
#include<stdio.h>
int main(void)
{
    int count,i,n;
    double grade,total;


    printf("Enter n: ");
    scanf("%d",&n);
    total=0;
    count=0;
    for(i=1;i<=n;i++){
        printf("Enter grade #%d: ",i);
        scanf("%lf",&grade);
        total=total+grade;
        if(grade<60){
            count++;
        }
    }
    printf("Grade average =%.2f\n",total/n);
    printf("Number of failures=%d\n",count);
    return 0;
}

/* 计算多分段函数 */
#include<stdio.h>
int main(void)
{
    double x,y;


    printf("Enter x:");
    scanf("%lf",&x);
    if(x<0){
        y=0;
    }
    else if(x<=15){
            y=4 * x/3;
    }
    else{
            y=2.5*x-10.5;
    }
    printf("f(%.2f)=%.2f\n",x,y);


    return 0;
}
    

/*求解简单的四则运算表达式 */
#include<stdio.h>
int main(void)
{
    double value1, value2;
    char op;
    printf("Type in an expression:");
    scanf("%lf%c%lf",&value1,&op,&value2);


    if(op=='+')
        printf("=%2.f\n",value1 + value2);
    else if(op=='-')
        printf("=%2f\n",value1 - value2);
    else if(op=='*')
        printf("=%.2f\n",value1 * value2);
    else if(op=='/')
        printf("=%.2f\n",value1 / value2);
    else
        printf("Unknown operator\n");


    return 0;
}

/* 统计字符， 包括英文字母·数字字符和其他字符 */
#include<stdio.h>
int main(void)
{
    int digit,letter,other;
    char ch;
    int i;
    digit=letter=other=0;
    printf("Enter 10 characters:");
    for(i=1;i<=10;i++){
        ch=getchar();
        if((ch>='a'&&ch<='z')||(ch>='A'&&ch<='Z'))
            letter++;
        else if(ch>='0'&&ch<='9')
            digit++;
        else
            other++;
    }
    printf("letter=%d,digit=%d,other=%d\n",letter,digit,other);



    return 0;
}
        

/* 查询自动售货机中商品的价格 */
#include<stdio.h>
int main(void)
{
    int choice,i;
    double price;

    
    for(i=1;i<=5;i++){
        /* 以下5行显示菜单 */
        printf("[1]Select crisps \n");
        printf("[2]Select popcorn \n");
        printf("[3]Select chocolate \n");
        printf("[4]Select cola \n");
        printf("[0]exit \n");



        if(choice==0)
            break;


        switch(choice){
            case1:price=3.0;break;
            case2:price=2.5;break;
            case3:price=4.0;break;
            case4:price=3.5;break;
             default:price=0.0;break;
        }
        /* 输出商品的价格 */
        printf("price=%0.1f/n",price);
    }
        printf("Thanks \n");


        return 0;
}

/*求解简单的四则运算表达式 */
#include<stdio.h>
int main(void)
{
    double value1,value2;
    char op;


    printf("Type in an expression:");
    scanf("%lf",&value1,&op,&value2);
    switch(op){
        case'+':
            printf("=%.2f\n",value1+value2);
             break;
        case'-':
             printf("=%.2f\n",value1-value2);
            break;
        case'/':
            printf("=%.2f\n",value1*value2);
            break;
       deflaut: 
            printf("Unknown operator\n");
            break;
    }


    return 0;  
}

/*求解简单的四则运算表达式 */
#include<stdio.h>.
int main(void)
{
    double value1,value2;
    char op;


    printf("Type in an expression:");
    scanf("%lf%c%lf",&value1,&op,&value2);
    if(op=='+')
        printf("=%.2f\n",value1+value2);
    else if(op=='-')
        printf("%.2f\n",value1-value2);
    else if(op=='*')
        printf("=%.2f\n",value1*value2);
    else if(op=='/')
        if(value2 !=0)
            printf("=%.2f\n",value1/value2);
        else
            printf("Divisor can not be 0!\n");
    else
        printf("Unknown operator!\n");


    return 0;
}

/* 判断整数的奇偶性 */
#include<stdio.h>
int main(void)
{
    int number;


    printf("Enter a number: ");
    scanf("%d",&number);
    if(number % 2==0){
        printf("The number is even. \n");
    }
    else{
        printf("The number is odd. \n");
    }


    return 0;
}